Severe PMS is a chronic and complex mood disorder that involves mood, behavioral and physical symptoms linked to the menstrual cycle with severity that disrupts functioning for as much as several weeks each menstrual cycle. Estimates indicate that 20-25% of menstruating women experience severe PMS. The efficacy of serotonergic antidepressants is clearly demonstrated for severe forms of PMS in short-term treatment trials. This study compares short-term treatment (4 months) and long-term treatment (12 months) with sertraline in a randomized, placebo-controlled design. The purpose is to determine how long medication should be continued following symptom relief, to what extent and how rapidly symptoms return after stopping medication, and whether there is any additional improvement with long-term treatment.